This invention relates to repair techniques for matrix addressed displays. More particularly, it relates to a matrix addressed display having apparatus for repairing and operating in the presence of line defects and to a method for effecting such repair. Of particular interest are active matrix liquid crystal displays, though the techniques taught herein apply to all matrix addressed displays having data drivers at both the top and bottom of the display.
A portion of a thin film transistor liquid crystal displays (TFTLCDs), also known as active-matrix liquid crystal displays (AMLCDs), are discarded from the manufacturing process because of data line defects. By repairing these defects the yield increases and the manufacturing cost decreases.
Defective data lines in TFTLCDs result from a number of mechanisms. Some occure due to metallurgical problems such as contamination during lithographic patterning of the data lines which manifest in opens or shorts. The shorts may occur between data lines themselves or between a data line and a gate line, or between a data line and some other part of the display circuit, such as the top plate. Other failures occur because some of the drivers on a data driver module fall below specification or fail, or because of a failure in the connection between the data lines on the glass and the driver chip.
Shorts can be removed by laser ablation, but some kinds of shorts (such as crossover shorts and top plate shorts) require that an open also be created by the laser ablation step. At present, the opens can then repaired as illustrated in FIG. 1.
In FIG. 1, the array portion 20 of an active matrix liquid crystal display is illustrated. A series of data lines 22 are each driven by one output of a data driver 24. For high resolution arrays which have a large number of lines per unit length, it is typical to have successive data lines 22 driven from the top and bottom of the array 20. Gate lines 26 are driven by gate line drivers (not shown). As is well known in the art, there is a thin film transistor located adjacent to each of the crossover points of every data line 22 and gate line 26 which drives a pixel or subpixel of the array 20. FIG. 1 includes a data line 22A which is driven from the top of array 20. Line 22A is open, that is, lacks electrical continuity due to a gap 28 so that transistors at intersections of data line 22A and gate lines 26 below gap 28 are not activated. This produces a so-called xe2x80x9cline defectxe2x80x9d which is highly visible and makes the panel totally unacceptable for sale as a commercial product unless an appropriate repair is effected. Conventionally a repair is made by mechanically connecting an insulated wire 30 between the top and bottom portion of the open data line. This method of repair is usually called a xe2x80x9cyellow wirexe2x80x9d repair, since this color of wire is often used to repair similar problems in printed circuit boards. The xe2x80x9cyellow wirexe2x80x9d jumper in FIG. 1 can physically run off the array substrate or be lithographically incorporated as a spare line on the array substrate. While correcting for opens, this type of repair introduces new problems. If the jumper wire is located on the glass, peripheral space on the substrate must be allocated, which increases the bezel area of the display package. Most importantly, jumper wires on the substrate must cross over or under other signal lines, and signal degradation will occur due to capacitive crosstalk with these other signal lines. If the jumper wire runs off the glass, signal degradation may occur due to other electromagnetic pickup. All of these problems also make it difficult to extend this repair method to repair more than one or two defective lines. Also, not all defects can be repaired in this manner. For example, defective data lines which are due to problems with the driver chip or driver chip connection usually require replacing the data drivers or discarding the entire defective panel.
It is a principal object of this invention to provide a matrix addressed display in which data line defects can be easily and inexpensively repaired.
It is another object of this invention to provide a method for easily and inexpensively repairing data line defects.
It is still another object of this invention to provide circuitry for manipulating pixel data so that an image is properly displayed when a data line repair is made.
It is yet another object of this invention to provide a method for manipulating pixel data so that an image is properly displayed when data line repair is made.
It is an additional object of the invention to provide a bus and repair pad design which is flexible, has a minimal crossover capacitance, and which is amenable to short-distance wire bonding.
In accordance with the invention several extra driver outputs are included in each data driver integrated circuit for repair as shown and described with respect to FIG. 2. These auxiliary drivers are connected to the defective lines via a metallurgical bonding technique. Open data lines are fixed by connecting auxiliary drivers, on the opposite side of the display, to the undriven ends of the open data lines. Weak/failed data drivers or low impedance loads can be corrected by adding a auxiliary driver in parallel with the existing driver, or opening the failed line and using one or more auxiliary drivers.
In the following discussion a pixel refers to a single picture element. In the case of a color display such as a TFT/LC display, the pixel is comprised of a trio of red, green and blue subpixels. In some cases four subpixels make up a picture element. In the case of a monochrome display, the smallest element in the display is the pixel, that is, there are no subpixels. It is also assumed in the discussion below that the data drivers in a color display accept three data elements at once, one each for red, green and blue. Though this is typical in the industry, other numbers of inputs can just as easily be accommodated in the techniques discussed.